The present invention relates to a method of fabricating quantum dot structures, particularly to a method of fabricating quantum dot structures by thermal etching.
A quantum dot is a zero-dimensional quantum structure having a size of about 100 .ANG.. According to quantum mechanical theory, the quantum dot structure should have better optical properties than a quantum well structure. In the quantum well structure, when the growth thickness reaches about 100 .ANG., quantization effects occur and thus force the electron energy along the growth direction to have discrete energy levels. With rapid growth in epitaxy techniques, high quality quantum well semiconductor materials have been successfully developed into quantum elements such as quantum well lasers, high electron mobility transistors, quantum well infrared detectors, . . . etc.
However, at present there still exists difficulties in applying prior art quantum well structures in practical applications. The major problems lie in the formation of surface states. Generally, the prior art fabrication of quantum dot structures, for example, U.S. Pat. No. 5,229,320 "Method for forming quantum dots" (referring to FIGS. 1a and 1b), uses photolithography and etching techniques on the quantum well structure epitaxy to expose quantum dots 32. This method produces a lot of surface states that are sources of non-radiactive recombination centers which lower the optical quality of the quantum dots. Currently, quantum dot structures produce less light intensity than quantum well structures while their optical linewidth is wider than for quantum well structures.